1. Field of the Invention
This invention relates to the mechanical arts. In particular, it relates to combustion engines.
2. Discussion of the Related Art
In an internal combustion engine, power is developed as a mixture of fuel and air is compressed by a piston in a cylinder and then ignited. In conventional engines, combustion occurs when the piston is at, or substantially at, the top dead center (or TDC). The period for combustion generally lasts for no longer than the time it takes the crank shaft to rotate about 2 to 4 degrees past top dead center.
The ignited gases force the piston down the cylinder. However, as the piston moves down the cylinder, the gases expand and cool and begin to lose their force.
The piston is attached to a connecting rod which in turn is attached to a crank shaft. It is the function of the connecting rod to convert the reciprocal motion of the piston being forced down the cylinder (a power stroke) and then returned back to top dead center (a compression stroke) into the rotary motion of the crank shaft.
It is desirable to cause ignition of the mixture of fuel and air at the moment of greatest compression, if maximum power and efficiency are to be obtained. The greater the compression or the tighter the squeeze the more heat that is generated during burning and the greater the force that can be used to drive the crank shaft. Consequently, ignition is timed so that the charge of fuel and air combusts when the piston is at, or substantially at, the limit of its upward movement in the cylinder.
If the ignition of the mixture of fuel and air occurs slightly before top dead center, then at the moment the mixture is ignited, some of the force developed by the explosion is wasted or lost, because it opposes the upward movement of the piston. If the ignition of the mixture occurs precisely at top dead center, there is also an initial loss of power, because the explosive force is expended along the connecting rod, which at TDC is directly aligned with the crank shaft. This loss of power, due to the alignment of the connecting rod, also occurs when the crank shaft is only a few degrees past top dead center.
Maximum efficiency is not obtained until the crank shaft rotates a sufficient amount to permit the explosive force to be expended in driving the crank shaft downwardly instead of laterally. It is, therefore, desirable to have the initial expansion occur when the crank shaft is well past dead center, so that the force of the expanding gases is utilized in the application of a turning force upon the crank shaft. However, in conventional engines, if the explosion is timed to occur when the crank is past dead center, the explosion will occur when the gases are not at peak compression and hence will not develop the maximum possible force.
In accordance with some embodiments of the instant invention, the period of high compression is extended beyond the relatively short period which occurs in conventional engines. This increase in the high compression period results in a constant volume burn and ensures that the initial expansion will not occur until the crank is well past top dead center. The advantages of constant volume combustion are outlined, for example, in Deglar, H. E., "Internal Combustion Engines", John Wiley & Sons, 1938, pp. 77 to 98 and Obert, E. F., "Internal Combustion Engines and Air Pollution", Harper & Row, 1973, pp. 166 to 175. In addition to maximizing the efficiency of the initial expansion, the extended period of high compression, or dwell, ensures that the fuel is completely burned, thereby further improving efficiency and materially decreasing undesirable exhaust products. The longer the constant volume burn, the cleaner, the quieter and the less polluting is the operation of an engine.